This invention relates to a method and apparatus for generating an enhanced tomogram, more specifically, a method and apparatus providing computer enhancement of a computer-assisted tomogram utilizing, for example, electrophysiological data.
Computer-assisted tomograms commonly referred to by the acronym CAT are currently utilized in diagnosis of the human body with particular emphasis on the central nervous system. CAT scanning units which generate such tomograms rely solely upon minute differences in tissue penetration to radiation as a source of information. During its extremely short life span, the CAT scanning unit has undergone rapid change and improvement such that the latest models have excellent resolution and display.
A parallel yet quite different computer-dependent system which is utilized for diagnosis of the central nervous system relies on electrophysiology. This system delineates the central nervous system functioning by analysis of cerebral activity utilizing an electroencephalogram commonly referred to as an EEG. Computer analysis of an EEG in terms of defining, determining and separating the spectrum of component wave forms of various frequencies and amplitude to develope a compressed spectral array is commonly referred to as CSA. Another technique relying upon evoked potentials is referred to as EPS.
As suggested above, an EEG wave form comprises a highly complex signal including a plurality of components and the EEG is merely a summation of all of these components. CSA is a presentation analysis of the EEG which, through the use of a computer, separates the components within the EEG envelop and displays these components. Standard EEG frequencies of 3-4 Hz. (delta); 4-8 Hz. (theta); and 12-30 Hz. (alpha-beta) are individually analyzed by CSA computation and the wattage in these bands computed. At the clinical level, a conventional EEG might visually appear quite normal yet the CSA display might reveal significant shifts to lower frequencies and thereby demonstrate a clear functional abnormality. In other words, without the CSA, the routine EEG may be a relatively insensitive tool. However, with CSA, the the EEG information can provide a sensitive method of assessing ongoing cerebral electrical activity.
Evoked potentials which are referred to as EPS are developed at cortical levels in response to a specific sensory stimulus. The stimulus may be sensory, auditory or visual. Under the usual conditions, the arrival of repetitive stimuli are buried in the ongoing EEG wave form and cannot be discerned. However, by utilizing computing modalities with time locked stimuli, an evoked response is developed. The evoked response has several components which are described in appearance latency as well as amplitude. This electrophysiologic method actually tests the functional capability of a neurocircuit by evaluating its response to a stimulus.
A CAT scanning unit has several limitations which may result in diagnostic errors. For example, isodense lesions may go undiagnosed since, for example, hematomas of sufficient age may have a radiographic appearance similar to that of the brain. Other diagnostic errors may arise out of metabolic disturbances such as general or local anoxia prior to actual infarction. Still other diagnostic errors arise out of CNS infections, seizures, hypoglycemia or systemic toxins (i.e., uremia, hepatic failure, etc.). In some instances, lesions, either single or multiple may be below CAT scanning resolution which can lead to a faulty diagnosis. Additional diagnostic errors may arise from bilateral lesions without shifting and/or extra-axial lesions such as certain subdural hematomas. In many instances, CAT scanning at a very early point in time after a stroke may be non-diagnostic. In other instances edema of the brain may be difficult to detect utilizing conventional CAT scanning techniques.
In summary, CAT scanning may be less than a perfect diagnostic tool. In no small part, this is due to the human incapability of the physician to detect subtleties in the CAT scan which might provide important diagnostic information.